C stdlib functions

stdlib.c

#include "stdlib.h"

/*
 * string_length:
 *  Returns the length of the pointer *s
 *  Same as strlen in <stdlib>
 */
unsigned long string_length(const char *s) {
    int c = 0;
    // dereference the pointer until EOF and raise the counter variable
    while (*s++) c++;
    return c;
}

/*
 * string_copy:
 *  Copies the string *src to *dst
 *  Same as strcpy in <stdlib>
 */
void string_copy(const char *src, char *dst) {
    while ((*dst++ = *src++) != '\0')
        ;
}

/*
 * string_duplicate:
 *  Returns the duplicate of the string *s
 *  Same as strdup in <stdlib>
 */
char *string_duplicate(char *s) {
    // start by allocating enough memory for the string + '\0'
    char *p = (char*)malloc(string_length(s) + 1);

    // if success we copy the string
    if (p != NULL)
        string_copy(p, s);

    return p;
}

stdlib.h

#ifndef STDLIB_H
#define STDLIB_H
extern unsigned long string_length(const char *s);
extern void string_copy(const char *src, char *dst);
extern char *string_duplicate(char *s);
#endif